April 15, 2024

TQI Exclusive: Photonics Illuminates Quantum Technology: Trends, Challenges and Opportunities

Klea Dhimitri

Application Engineer, Hamamatsu Corporation

What image comes to mind when you hear the words “quantum technology”?

What about the “quantum computer”?

You’re most likely thinking of the golden chandelier often found in a large dilution refrigerator that quantum computing players like IBM and Google use to cool and operate a superconducting qubit. However, there is one core technology that is often overlooked when we talk about quantum computers: and that is photonics. Dr. Bob Sutor, who spent more than two decades at IBM Research in New York working on and leading IBM’s efforts in quantum computing, knows his way around big cyrostats. Currently, Dr. Sutor is the Vice President and Chief Quantum Advocate at Infleqtion, where at an event he stated:

“Photonics is huge. Photonics is the core of the future quantum infrastructure and without good growth of the photonics industry that reduces the cost and size of, for example, photonics integrated circuits, none of this will work beyond machines the size of a toy that are disconnected from each other.” [1].

This article aims to shed light on how photonics is currently enabling multiple areas in emerging quantum fields such as quantum computing, quantum communication and networking, and quantum sensing, as well as address the challenges and opportunities ahead.

The quantum technology landscape can be divided in several ways, but in this article we will divide the field into four pillars: 1) Quantum Computing and Simulation 2) Quantum Communication and Networking 3) Quantum Metrology and Sensing and 4) Fundamental Research. Subsections within each pillar that use photonics are highlighted in yellow in Figure 1. The figure illustrates that more than 2/3third of the field uses photonics and photonics plays an important role in the quantum technology landscape.

Figure 1: Overview of the pillars of quantum technology where the use of photonics is highlighted in yellow.

Role of photonics in quantum computing and simulation

Scientists are investigating a variety of qubit modalities to create a fault-tolerant universal quantum computer, but for several qubit modalities photonics is the core of their toolbox. Photonics has a wide range of capabilities, such as the ability to apply gate operations, confine atoms in a matrix, and detect qubit states (either 0 or 1) through low- or lack-of-light fluorescence from trapped ions. or neutral atoms. Qubit modalities, such as photonic quantum computing, make full use of the photon. using a property of the photon to build a qubit. The vision of photonic quantum computing is the complete optical table, from light sources to optics and photon detectors on a chip. [2].

Scaling and fidelity are the main drivers for the development of photonic components in qubit modalities, such as trapped ions, neutral atoms, and photonic qubits.

The current trapped ion infrastructure needed to operate a small chain of tens of ions typically occupies two optical tables. [4]. The development of photonic components such as photonic integrated circuits (PICs) is of interest to trapped ion developers, for example, because it could help make the modality more scalable. Gathering more ions while each ion is precisely controlled could help scale the processor without a large, cumbersome infrastructure to scale along with it. [7].

Figure 2: Blatt Lab Trapped Ion Setup

Role of photonics in communication and quantum networks

The photon is a tried and tested carrier for sending information over long distances, as seen in classical optical communication networks. The appeal of the photon in quantum communication and networks is that a qubit can travel long distances. [6] as well as notifying users when a spy is listening. Devices such as quantum random number generators (QRNGs) that produce truly random keys used in quantum communication protocols could also be realized using light sources and detectors. [5].

Quantum key distribution and quantum networking hardware also rely on photonics, such as excitation or pump lasers for photon sources to emit photons in optical fibers, for example, and detectors ranging from single-photon detectors to photodiodes for detect them at the receiving end of the fiber.

Terrestrial quantum networks have limited distance due to fiber optic losses and lack of quantum repeaters. Space and satellite networks have limitations in aperture and diffraction loss. The main driver for the development of photonic components for quantum communication is to preserve photons over long distances.


Figure 3: Different types of quantum networks

Role of photonics in quantum metrology and sensing

The field of quantum metrology and sensing focuses on precise probing of the environment in terms of measurement, such as electric, magnetic, and gravitational fields, as well as timing and positioning. The information measured by quantum sensors could be communicated using fluorescence. In the case of a nitrogen vacancy (NV)-based magnetometer, the different fluorescence intensities are related to the intensity of the magnetic fields present. The main drivers for the development of quantum sensing photonic components are size, weight, power and cost (SWaP-C) for field-deployable applications.

Market opportunity for photonics

The market for quantum systems is not currently high, but the market for photonic components is and is promising. More than half of the bill of materials (BOM) cost of quantum systems goes toward lasers, while the rest is split between detectors, modulators, and other components. Currently, the largest market for photonic components is under investigation, with an estimated value of $171 million for lasers and $33 million for photonic components including detectors, modulators and other components. Starting in 2025, photonic components for quantum products manufactured by OEMs are predicted to be larger than photonic components used in research. [8].

Photonics challenges in quantum technologies

One of the photonic challenges for quantum technologies is the construction of single-photon sources that contain all the desired features for applications such as quantum key distribution and some forms of photonic quantum computing. [9]. Photonic integrated circuits (PICs) are considered the holy grail of quantum technology. However, PICs still present some challenges, such as incorporating all optical components, including lasers and detectors, on a chip, as well as the cost of a PIC production line. These production lines need high volume to keep costs manageable and it is unclear if quantum applications will scale and, if so, when. [10]

Ongoing advances in photonic components will be critical to realizing quantum systems and building them for the quantum 2.0 era.

References

[1] YouTube video by Bob Sutor. https://www.youtube.com/watch?v=sRAZ8PJzzLY 6:28 to 6:56

[2] Masuda, A. (2019). https://www.news.ucsb.edu/2019/019679/pushing-quantum-photonics

[3] Choi, C. Q. (2021). https://spectrum.ieee.org/race-to-hundreds-of-photonic-qubits-xanadu-scalable-photon

[4] Jurcevic, P., Mandelbaum, R. (2021). This is how ion trap quantum computers work. The quantum aviary. https://thequantumaviary.blogspot.com/2021/03/heres-how-ion-trap-quantum-computers.html [5] Jennifer Aldama, Samael Sarmiento, Ignacio H. López Grande, Stefano Signorini, Luis Trigo Vidarte and Valerio Pruneri, “Integrated QKD and QRNG photonic technologies”, J. Lightwave Technol. 40, 7498-7517 (2022)

[6] Awschalom, D.D., et al. https://doi.org/10.2172/1900586

[7] Niffenegger, R.J., Stuart, J., Sorace-Agaskar, C. et al. Integrated multi-wavelength control of an ion qubit. Nature 586, 538–542 (2020). https://doi.org/10.1038/s41586-020-2811-x

[8] Tematys Photonics@Quantum: Technologies for Quantum Systems Report (April 2022)

[9] OIDA, “OIDA Quantum Photonics Roadmap: Every Photon Counts,” Optical Industry Report, 3 (2020)

[10] Davis, S et al. Piercing the fog of quantum-enabled laser technology (QELT) A report based on a QED-C enabling technology workshop. QED-C. (2018).

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